Timing of brain damage and verbal-performance IQ tilts

Abstract

Sir, Anderson et al. (2009) refuted the Kennard Principle, which states that the immature brain is more plastic and less vulnerable to insult than a mature brain (Montour-Proulx et al. , 2004); however, there are important errors in Table 5 of their paper. The IQ data for their six age subgroups do not tally with the total group figures in the last column of Table 5. In each of these six subgroups, the IQ figure in the last row is intermediate between the first two rows, so clearly must be the full scale IQ, and not performance IQ as stated (V, P and FS refer to verbal, performance and full scale IQs on the Wechsler Intelligence Scales). One would then assume, as is usually reported, that the first subgroup row is verbal IQ, the second performance IQ and the third full scale IQ. However, there are two major problems with this reading: 1. the mean figure for full scale IQ for the whole group (last column in Table 5), intermediate between verbal IQ and performance IQ, is now in row 1 and not row 3. The mean total group figures as printed do not correspond to subgroup row order from Table 5 (FS/V/P), to the more usual proposed order (V/P/FS), or to that expected from the previous literature (FS/P/V). 2. In all six subgroups, verbal IQs would be lower than performance IQs. For those aged 3–6 years at lesion, verbal IQ would be 94 and performance IQ 100; for age 7–9 years, verbal IQ would be 94 and performance IQ 102; for 10–16 years, verbal IQ would be 95 and performance IQ100. For the total group of 160 children, the figures in Table 5 claim a mean verbal IQ of 86 (see also p. 49) and performance IQ of 91. It was …